Expression of Sclerostin in Osteoporotic Fracture Patients Is Associated with DNA Methylation in the CpG Island of the SOST Gene.

Yanming Cao,Haibin Wang,Liangliang Xu,Bin Wang,Ding Wang,Yamei Liu,Wei He,Caiyuan Mai,Peng Wang,Dongxiang Zhan,Qiushi Wei

doi:10.1155/2019/7076513

Abstract

Purpose SOST gene is one of the key factors in regulating bone absorption. Although there are reports showing diverse transcription factors, epigenetic modification could be responsible for regulating SOST gene expression. There is still little exploration on promoter methylation status of SOST gene in osteoporotic bone tissues. The aim of this study is to investigate the involvement of CpG methylation in regulation of SOST expression in patients with primary osteoporosis. Methods The diagnosis of osteoporosis was established on the basis of dual energy X-ray absorptiometry to measure BMD. All femoral bone tissues were separated in surgeries. After extracting total RNA and protein, we checked the relative expression levels of SOST by quantitative real-time PCR and western blot. Also, immunohistochemical staining was performed to observe the expression of SOST protein in the bone samples. The genomic DNA of non-OPF (non-osteoporotic fracture bone tissues) and OPF (osteoporotic fracture bone tissues) were treated by bisulfite modification, and methylation status of CpG sites in the CpG island of SOST gene promoter was determined by DNA sequencing. Results SOST gene expression in the non-OPF group was lower than that in OPF group. Bisulfite sequencing result showed that SOST gene promoter was slightly demethylated in the OPF group, as compared with non-OPF group. Conclusion Our study demonstrated that DNA methylation influenced the transcriptional expression of SOST gene, which probably may play an important role in the pathogenesis of primary osteoporosis.

Highlights

Sclerostin (SOST) is the secreted glycoprotein encoded by the SOST gene
We found that the expression level of sclerostin was much higher in the OPF group (Figures 1(b) and 1(c)), which is consistent with the quantitative real-time PCR result
The staining of bone samples with a specific sclerostin antibody confirmed that SOST was highly and expressed in osteocytes in OPF group (Figures 2(a) and 2(b))

Summary

Introduction

SOST mRNA and protein are expressed in osteocytes which are the most prevalent cells in mineralized bone [1, 2]. It is a potent inhibitor of bone formation which antagonizes the canonical Wnt signaling by binding to Wnt coreceptors LRP-4, LRP-5, and LRP-6. Mutations in the SOST gene are associated with disorders such as sclerosteosis and van Buchem disease characterized by increased bone mass [5, 6]. The SOST knockout mice have a high bone mass phenotype characterized by significant increases in BMD (bone mineral density), bone volume, bone formation, and bone strength [7].

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